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Freebore Pneumatic Effect Cannon
The Freebore Pneumatic Effect Cannon was a large weapon type used by The Royal Allegiance. Usage The Freebore Pneumatic Effect Cannon system, or FPEC, was employed on all Allegiance cannons of calibre greater than 45mm. However, it only made a substantial difference when used on larger cannons, such as the L82 Cannon and the L120 Cannon. As a result it was used to great effect on larger armoured vehicles which could mount larger main guns. The most widespread and effective use of the FEPC was the M560A2 Crusader's main gun, the L120 Cannon. The barrel was subjected to more stresses than standard smoothbore or rifled ones but was much more efficient and allowed for higher velocity, accuracy and range than conventional barrel types. The round would be subjected to a much more constant acceleration down the barrel, as well as markedly reduced friction. The FPEC system allowed a much flatter ballistic trajectory, meaning longer ranges were possible with the same degree of accuracy. Design An FPEC cannon was quite different to its predecessors, which used the somewhat questionably efficient 'rail and groove' method, which allowed for the entire length of the groove to be open to both the front of the round and the propellant gases. This led to any turbulence allowing propellant gas to escape and increasing the area that the gas expanded into, decreasing the cannon's overall efficiency. Replacing this method was a much simpler to manufacture method of one hundred and twenty canted two centimetre cells four millimetres deep, arranged in twelve rows of ten cells. This method allowed for a heavy barrel to be drilled out instead of constructed from several individual parts and then constructed into a barrel, which would be only as strong as the welds that held it together. In a normal smoothbore or rifled barrel in a state of rest, it was filled with air also in a state of rest. When a round was fired the vacuum generated by the mass of air being distorted by the movement of the round was sucked around the aerodynamic shape of the round. The path of least resistance for the first 'block' of air in front of the projectile was to be pushed to the side, and the remaining turbulence would force the air into one of the one-hundred and twenty cells. The air remained pressurised in the cells by both physical occupation of space and air turbulence. This method also prevented propellant gas from behind the round from slipping out, as the inner bore was fully occupied by either the sabot or projectile. As long as the pressure of the main propulsion remained constant, it would be higher than the air in the cells, but as it reached the end of it, pressure dropped. The round in a normal cannon would begin to decelerate slightly due to friction, but, with the lowered pressure of the main tube in a Freebore cannon, the pressurised atmosphere in the cells were now of equal level with the propellant gas and would expand removing the pressure gap and continuing applying a steady pressure all along the round's path down the barrel. The round therefore received a constant acceleration as it moved along the barrel, and also encountered far less friction than a full bored gun due to decreased surface area contact, and had a much more accurate shot with a flatter ballistic trajectory.